"Things are still growing, but not at the rate that they used to," said Jeff Robinson, a senior fiscal analyst who co-authored the report.

Though the 2017 budget year ended June 30, Gov. Kim Reynolds has said she will wait to address the shortfall until the state officially closes its accounting books at the end of September.

Because money is still moving, Robinson said, the $104 million shortfall could grow or decline before Sept. 30. Tax refunds, for example, will continue to be paid out in July and August even though they're attributed to the 2017 budget. Other revenue could come in as companies and others pay what they owe.

Reynolds has the authority to borrow up to $50 million from the state's reserve accounts to cover the imbalance, but anything beyond that would require a special session of the Iowa Legislature.

Robinson said it would be unusual, though not impossible, for the state to find enough money between now and the end of September to stave off a special session.

"Most years, no, there’s not $55 million worth of variance in there," he said. "Not normally."

Democrats were quick to criticize Republican leaders, who control the House, Senate and governor's office.

"Continued borrowing doesn’t fix the fact that they’ve created these huge tax breaks going to out-of-state companies; it doesn’t rein in tax credits," said Rep. Chris Hall, the top Democrat on the House Appropriations Committee. "They've already cut state agencies to their bone."

Faced with continued revenue stagnation, legislators made mid-year cuts to the 2017 budget and approved a 2018 budget that scaled back spending even further. And although borrowing helped cover the immediate shortfall in 2017, that money will have to be repaid in 2018 and 2019, likely forcing further cuts.

House Appropriations Chair Rep. Pat Grassley, R-New Hartford, noted that other state's also are having difficulty accurately projecting revenue.

"This is a national trend with 32 other states experiencing this same problem," he said in a statement. "But (in Iowa) it is the fourth consecutive year where the forecast has been higher than actual revenue collected. We need to re-examine our process and find ways to improve its accuracy."

The report issued Monday showed growth in tax revenue from individuals and corporations, but sales- and use-tax growth increased by just 0.1 percent over the course of the year.

David Roederer, director of the Department of Management, has attributed much of that stagnation to the proliferation of online sales.

But Robinson previously issued a separate report blaming the stagnation on a controversial tax law change that benefits manufacturing companies by exempting a wider array of goods they use from sales and use taxes. Robinson said sales- and use-tax revenue began flattening out just as that change took effect, estimating it could result in reduced revenue of about $100 million, or nearly $80 million more than expected.